diff -r 22a46f05ce23 Lib/urllib2.py
--- a/Lib/urllib2.py	Wed Sep 24 20:22:24 2014 -0400
+++ b/Lib/urllib2.py	Thu Sep 25 15:20:18 2014 +0200
@@ -1045,7 +1045,8 @@
             H = lambda x: hashlib.md5(x).hexdigest()
         elif algorithm == 'SHA':
             H = lambda x: hashlib.sha1(x).hexdigest()
-        # XXX MD5-sess
+        else: # MD5-sess
+            raise NotImplementedError("Unsupported Digest Authentication Algorithm '%s'" % algorithm)
         KD = lambda s, d: H("%s:%s" % (s, d))
         return H, KD